The Object Group Design Pattern

Abstract

This paper describes "Object Group", an object behavioral pattern for group communication and fault-tolerance in distributed systems. The Object Group pattern supports the implementation of replicated objects, of load sharing, and of efficientmulticast communication over protocols suchasIP-multicast or UDP-broadcast. Application areas of the pattern are fault-tolerantclient/server systems, groupware and parallel text retrieval engines. Events within an Object Group honor the Virtual Synchrony model. With Virtual Synchrony, the size of an object group can be varied at run-time while client applications are interacting with the group. A replicated state remains consistent in spite of objects entering and leaving the group dynamically and in spite of failures. The Object Group pattern has been implemented in the Electra and in the Orbix+Isis CORBA Object Request Broker.